1. Field of the Invention
The present invention relates to an electric power steering device that gives a steering assisting force by using a motor and a method for controlling the electric power steering device.
2. Description of the Related Art
In a related electric power steering device adapted to give a steering assisting force by using a motor, the steering assisting force is changed according to operating conditions, such as steering torque and a vehicle speed. However, in the case of employing such a related electric power steering device adapted to simply change the steering assisting force according to the operating conditions, when a steering speed is changed, a steering feeling is worsened under the influence of the inertia of a moving part of a steering system, which includes the motor. Thus, the following countermeasure is taken. That is, a rotation angular speed of the motor is obtained according to the inter-terminal voltage, electric current, resistance, counter-electromotive-force constant of the motor thereof. Then, an output of the motor is corrected according to a rotation angular acceleration computed from the obtained rotation angular speed in such a manner as to compensate for the influence of the inertia of the moving part on steering. However, the obtained rotation angular acceleration of the motor lags behind an actual angular acceleration of the steering wheel, which is caused by actual steering. Consequently, the influence of the inertia cannot be compensated for with timing with which such influence should be compensated for. Thus, the steering feels heavy.
Thus, there has been proposed a related power steering device adapted to compensate for the influence of the inertia according to an angular acceleration of a steering wheel, which corresponds to a sum of a change is acceleration of steering torque and a rotation angular acceleration of a motor, instead of a rotation angular acceleration of the motor (see Patent Document 1).
[Patent Document 1]
Japanese Patent No. 2,694,213.
However, the related device has encountered problems that when a steering direction is reversed at high speed, the related device cannot accurately compensate for the influence of the inertia with timing with which the device should compensate for the influence thereof, and that a steering feeling is worsened.